1. Field of the Invention
The present invention relates to capacitive deionization technology, and more specifically, it relates to capacitive deionization (CDI) electrode fabrication and CDI reactor configurations that reduce capitol costs, increase efficiency, and enable the replacement of electrode surface accompaniments.
2. Description of Related Art
Capacitive deionization is a technology developed to remove ions in solution by bringing the solution between two electrodes of opposite charge. The positive ions are attracted and migrate to the negative electrode material, and the negative ions behave similarly with the positive electrode. Several different approaches to this technique have been proposed (and patented by J. Farmer, M. Andelman and others).
One key to effective treatment using capacitive de-ionization is maximizing the surface area of the electrode surface material. A larger electrode surface area increases the number of locations or sites to which ions may attach. As the available attachment sites fill, the efficiency of ion removal decreases. In an effort to maximize electrode surface area, several materials (e.g., carbon aerogel) have been used as electrode surface accompaniments; however, many other electrode surface materials have yet to be tested.
Another key element in the CDI approach is the maintaining of electrode integrity. Electrode material in the presence of an electrical field and a conductive solution will tend to oxidize at the cathode and reduce at the anode causing rapid reduction of electrical and/or mechanical properties and introduction of the electrode material (e.g., Cu, Fe) into solution. Materials that resist degradation are typically precious metals like gold, and titanium. Past experiments by Farmer have utilized titanium electrodes with carbon aerogel epoxied to the surface.
As with most applications being developed for commercial use, capitol costs play a major role in determining technology efficiency. The electrode substrate material used during development of CDI at Lawrence Livermore National Laboratory (LLNL) was epoxied to the surface of the titanium electrodes. This process is time consuming and may affect the performance of the carbon aerogel due to the seepage of epoxy within the aerogel matrix. Also, titanium is expensive and, without being isolated, posed an increased risk of short-circuiting between electrodes and a shock hazard.
Prior designs for capacitive de-ionization (CDI) (by Farmer) have specified the use of titanium plates with a high surface area substrate material attached to the surface to be used as the electrodes. This was an appropriate design for the initial testing but it had some drawbacks. Titanium is expensive. The electrodes required extensive machining. Adhering the substrate material to the titanium surface was time consuming, and may have resulted in a reduction in surface area due to infiltration of the epoxy within the substrate matrix. There was a high risk of short-circuiting between electrodes and a shock hazard if any metal object touched the CDI reactor.
It is desirable to provide a new electrode design that uses less expensive materials, has a reduced fabrication costs, allows for easy replacement of electrode substrate material without the use of glue and has a configuration that is intrinsically safer.